This invention is directed to a sound simulation system, and, in particular, to a multi-channel sound simulation system for interfacing between a stereo signal source and a plurality of loudspeakers for processing a stereophonic signal to be applied to a pair of primary and at least a pair of secondary loudspeakers in a home stereo system. This invention serves to provide a sense of surround sound ambiance in a listening room.
The development of the surround sound system commonly sold under the trademark DOLBY.RTM., by Dolby Laboratories, Inc. of San Francisco, Ca., for the motion picture and music industries has created a need for new systems to decode the DOLBY.RTM. encoded sound. The DOLBY.RTM. system involves a two-step procedure in which the original recording is encoded to combine multiple channels of information into two recorded channels. This encoding involves the mathematical manipulation of both the phase and frequency characteristics of the original sound. The resulting two-channel information is then recorded in the usual manner onto tapes, discs or the like. Upon playback, the DOLBY.RTM. system decoder mathematically reconstructs the original multiple channel signals from the two-channel source. Heretofore, implementation of the DOLBY.RTM. system required a minimum of four channels of amplification to accomplish this task. Accordingly, precise reconstruction of the multiple channels of information was complicated and required expensive electronic equipment capable of creating four distinct channel signals.
One such attempt at producing at least a four channel output from a stereophonic input is U.S. Pat. No. 3,697,692 (Hafler). The Hafler patent discloses a system for interfacing between a two-channel stereo signal and at least four loudspeakers for producing four output signals to be input into four loudspeakers, such that when the four loudspeakers are placed at the corners of a quadrilateral area, and are positioned to face toward the interior of the area, a listener positioned interior of the area perceives the sound to be directed from the four sides of the area, rather than from the four corners where the loudspeakers are located.
However, one disadvantage of systems such as Hafler is that the secondary speakers are often directly perceived by the listener. Thus, the listener receives a distinct perception of the presence of secondary speakers. Secondly, DOLBY.RTM. encoded sound sources will often appear "bright", possessing too much high-frequency response, to listeners who do not have the actual DOLBY.RTM. licensed equipment for its decoding. Thirdly, information which should "appear" localized front and center is often improperly positioned. Accordingly, reduction in the "brightness" of the DOLBY.RTM. encoded source and the perception of the presence of separate secondary and/or tertiary loudspeakers is desired, as well as a method for improving the center image reproduction.